Copper sulfate generates copper ions in an aqueous solution thereof and shows a very strong bactericidal action or effect. Therefore, it has been used as an agricultural chemical over not less than 100 years, while making use of the foregoing characteristic properties. However, the copper ion likewise has a strong action of causing damage from agricultural chemicals (a phytotoxicity or a chemical injury) on a plant body. For this reason, there have been proposed a variety of means to use the same while masking the most use of the strong bactericidal action thereof and preventing any adverse effect thereof on the plant body. An example thereof is to mix copper sulfate with quick lime and the mixture has long been known as Bordeaux mixture and has been put in practical use. In this respect, however, the influence of the copper may vary depending on the kinds of plants. Accordingly, not only it would be necessary to change the mixing ratio of copper sulfate and quick lime for every particular plants, but also a technology of a high level would be required for the preparation of each particular mixture.
To this end, there has been designed the so-called premix Bordeaux. In this premix, a basic copper chloride or a basic copper sulfate is substituted for copper sulfate to thus inhibit any release of copper ions from the same. However, copper ions are rapidly released out of the premix due to, for instance, rainwater and this may give rise to damages from the agricultural chemical, in most of cases, even when using such premix Bordeaux. For this reason, calcium carbonate (such as a product sold under the trade name of kurefunon (calcium carbonate content: 95%)) is added to a spraying solution to further increase the basicity thereof and to thus prevent any release of copper ions from the premix. However, it is difficult to completely prevent the occurrence of any damage from agricultural chemicals even if the basicity of the premix is thus increased due to, for instance, a rainfall immediately after the spray of the same. In such a formulation, the release of copper ions is prevented by making the formulation basic and therefore, if the formulation is acidified by, for instance, acid rain, a large quantity of copper ions are released from the same and this would in turn lead to the occurrence of any damage from agricultural chemicals.
As has been discussed above, any conventional copper-containing formulations have been made strongly basic to thus prevent any release of copper ions for fear that any damage from agricultural chemicals may occur. Accordingly, in order to achieve or ensure a desired plant disease control effect, such a formulation should be sprayed on plants in a large quantity on the order of, for instance, 5 kg/ha. If a copper-containing formulation has been sprayed thereon over a long period of time, copper may accumulated in the soil and the release of the copper accumulated in the soil would cause the pollution of watercourses and drinking water.
When copper sulfate is mixed with sodium pyrophosphate or potassium pyrophosphate in water in a molar ratio of 2:1, copper pyrophosphate is formed, which is hardly soluble in water. Thus, the copper pyrophosphate is hardly soluble in water and therefore, it has never been used as an active component for an agricultural chemical. Moreover, it has been known that the copper pyrophosphate may be converted into a water-soluble one through the formation of a double salt or a complex salt with sodium pyrophosphate. Up to this time, however, there has not been any report concerning the bactericidal activity of this reaction product against vegetable pathogenic bacteria and/or fungi.
Japanese Un-Examined Patent Publication (hereunder referred to as “J.P. KOKAI”) Hei 8-165213 discloses the effect of copper metaphosphate on Escherichia coli. In this respect, however, the copper metaphosphate is one prepared by heating ammonium dihydrogen phosphate and copper oxide at 800° C. and therefore, it comprises meta-phosphoric acid and copper in amounts of equal chemical equivalents.
J.P. KOKAI Hei 6-40806 discloses a bactericidal and insecticide composition containing a coated agricultural chemical prepared by coating 100 pars by mass of an effective component for the agricultural chemical with 0.1 to 10 parts by mass of a fatty acid ester of an aliphatic polyhydric alcohol and/or a phospholipids and 0.01 to 10 parts by mass of a pasting or sizing agent. As such a component for the agricultural chemical, there is listed, for instance, copper sulfate and examples of such pasting agents disclosed therein are sodium polyphosphate, potassium polyphosphate and sodium metaphosphate, but the mixing ratio of copper sulfate to, for instance, sodium polyphosphate is quite low and more specifically, the mixing rate of copper sulfate and, for instance, sodium polyphosphate is 0.01 to 10 parts by mass of the latter relative to 100 parts by mass of the former.